In many instances it is desirable or necessary to regularly monitor the concentration of particular constituents in a fluid. A number of systems are available that analyze the constituents of bodily fluids such as blood, urine and saliva. Examples of such systems conveniently monitor the level of particular medically significant fluid constituents, such as, for example, cholesterol, ketones, vitamins, proteins, and various metabolites or blood sugars, such as glucose. Diagnosis and management of patients suffering from diabetes mellitus, a disorder of the pancreas where insufficient production of insulin prevents normal regulation of blood sugar levels, requires carefully monitoring of blood glucose levels on a daily basis.
In vivo analyte monitoring systems include an in vivo analyte sensor. At least a portion of the sensor is positioned beneath the skin surface of a user to contact bodily fluid (e.g., blood or interstitial fluid (ISF)) to monitor one or more analytes in the fluid over a period of time. This is also referred to as continuous analyte monitoring in that the sensor remains positioned in the user for a continuous period of time. Other forms of testing include in vitro testing—e.g., by withdrawing blood from a patient and applying the blood to a test strip for insertion into an analyte monitoring device, such as a glucose meter.
ISF glucose may lag in time behind blood glucose. That is, if the blood glucose is falling and reaches a low point, the ISF glucose will reach that low point some time later, such as 10 minutes for example. Traditionally, the goal of analyte monitoring systems is to provide results that approximate blood glucose concentrations since blood glucose concentrations may better represent the glucose level in the patient's blood.